L-theanine

L-theanine is thought to result in a possible calming effect by competing with L-glutamic acid at the binding site for glutamate receptors in the brain. Experimental studies in rats demonstrated an increase in dopamine and 5-HT (serotonin) after intake of theanine. A single human study also demonstrated that L-theanine prevented an increase in blood pressure and heart rate in response to psychological and physical stressors. However, another prospective RCT did not demonstrate a significant improvement in people with generalized anxiety disorder associated with L-theanine, while a meta-analysis found an overall benefit in people with various mental disorders (Moshfeghinia et al., 2024). Thus, reports of efficacy are mixed, and much remains to be elucidated regarding efficacy in veterinary patients.

In veterinary medicine, objective behavioral measures in laboratory models have suggested that L-theanine can reduce fearful behavior toward unfamiliar human beings, with treated dogs showing slightly greater human interaction and approach than placebo controls (Joseph et al., 2010). Clinical studies in client-owned dogs have also indicated potential benefits for situational phobias. Specifically, L-theanine has been shown to significantly decrease global anxiety scores and the time required for dogs to return to a baseline normal state following storms (Pike et al., 2015). Furthermore, when used in conjunction with behavioral therapy, L-theanine has been associated with a reduction in the intensity of specific phobic symptoms such as panting, drooling, and vocalizing during noise events, although these clinical improvements are not always accompanied by a measurable change in blood cortisol levels (Michelazzi et al., 2010).